The present invention relates generally to a retractable covering or separating device for motor vehicles, and more particularly to a retractable covering or separating device that is operated by an electric motor.
There are a number of retractable covering (or separating) devices used in motor vehicles, which can be rolled up or folded and are driven by an electric motor. Examples of such covering device are windup rollers for rear windows, such as described in DE 44 12 557. Many of these covering devices have a windup shaft on which a web, such as a windup roller web or a separating screen, is fastened along an edge and can be rolled up onto the shaft. The windup shaft is pre-stressed in the winding direction of the respective web by means of a spring drive, and the web is pulled off or unwound from the windup shaft with the aid of an electric motor against the action of the spring.
Two pivot levers are provided in the above mentioned rear window windup roller, which are seated next to the windup shaft and are rotatable around an axis extending perpendicularly with respect to the axis of the windup shaft. The pivot levers are moved with the aid of two coupling rods. One end of each coupling rod is fastened by means of a hinge to one of the pivot levers, and the other end of each coupling rod is connected to a respective crank pin, which are in turn fixed on the output shaft of the gear motor. It is also known to use a kinematic reversal, wherein the pivot lever is pre-stressed by means of springs in the unwinding direction, while the windup roller itself is driven by the electric motor. Another variation consists of foldable covering devices, wherein a hoop is driven. Typically, the hoop travels the greatest distance during retraction and extension.
A time function element is typically used for controlling such rear window windup roller and covering devices, which puts the motor into motion for a defined length of time when activated. By means of the time function element, it is intended to relieve the burden on the driver of the vehicle. By a brief actuation of the appropriate directional switch, the windup roller is either completely retracted or completely extended. The driver is not required to either operate the activating button for an appropriate length of time or to remember to bring the switch back into its off position.
In order for this type of control to operate properly, it is necessary that the mechanical drive be sufficiently robust to withstand, without being destroyed, the maximum torque the motor can exert in case of blockage. For this reason, the mechanical parts of the drive systems are typically greatly over-dimensioned, particularly with respect to movement in connection with which pressure forces occur, which could lead to warping of the respective rods. Crank pins are another weak point, which cannot be permitted to break off in case of blockage.
In view of the foregoing, it is an object of the invention to create an improved drive system for a motorized retractable covering device that is able to shut the electric motor off before excessive forces can occur. As used herein, the term xe2x80x9ccovering devicexe2x80x9d is intended to include separating devices.
In accordance with this and other objects of the invention, the present invention provides a drive system for a retractable covering device used in a motor vehicle that is operated by an electrical motor to move between two end positions. The drive system includes a current sensor for detecting the current applied to the electric motor and uses the detected current information to decide when to shut off the electric motor. To that end, the drive system includes a control device that monitors the current and measures at least one electrical current parameter when the electric motor is supplied with current to move the covering device to leave one end position toward another end position. The value of the electrical current parameter measured in this way is stored as a reference value, and subsequently measured values of the electrical current parameter are compared with the reference value in order to switch off the current for the electric motor when the comparison between the reference value and a subsequently measured value of electrical current parameter meets a pre-defined condition.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: